What are the ramifications of the word "v'Hisvadah"?
Rashi (in Shevu'os): All Chata'os and Ashamos only atone after the sinner has done Teshuvah.
Why does the Torah mention Viduy specifically here, and not by any of the other Chata'os?
Ramban #1, Moshav Zekenim #1: Because, Shevu'as ha'Eidus, unlike the other Chata'os, is Chayav even be'Meizid.
Ramban #2 (citing the Sifri Zuta), Moshav Zekenim #2: The Mitzvah of Viduy actually applies to all the Chata'os mentioned in the Parshah, and the Torah mentions it here because Shevu'as ha'Eidus and Shevu'as Bituy (in Pasuk 4) are not subject to Kares. 1 All the more so Viduy is needed for Chayavei Kerisus!